Level shifter

ABSTRACT

A level shifter includes a buffer circuit, a first shift circuit, and a second shift circuit. The buffer circuit provides a first signal and a first inverted signal to the first shift circuit, such that the first shift circuit provides a second signal and a second inverted signal to the second shift circuit. The second shift circuit generates a plurality of output signals according to the second signal and the second inverted signal. The first shift circuit includes a plurality of first stacking transistors and a first voltage divider circuit. The first voltage divider circuit is electrically coupled between a first system high voltage terminal and a system low voltage terminal. The first voltage divider circuit is configured to provide a first inner bias to gate terminals of the first stacking transistors.

RELATED APPLICATIONS

The present application is a Divisional Application of the U.S.Application Serial Number 17/517,093, filed Nov. 02, 2021, which claimspriority to Taiwan Application Serial Number 110117124, filed May 12,2021, all of which are herein incorporated by reference in theirentireties.

BACKGROUND Field of Invention

The present disclosure relates to a level shifter. More particularly,the present disclosure relates to a level shifter that realizes anincreased voltage difference between an input voltage domain and anoutput voltage domain.

Description of Related Art

In today’s technology, a level-shifting circuit is utilized in acircuitry that demands different voltage requirements among somecircuits. A level shifter can usually receive an input signal switchedin a first voltage domain, and output an output signal corresponding tothe input signal and switched in a second voltage domain. The secondvoltage domain may be different from the first voltage domain. How toincrease the shift range of the output signal has become an importantsubject.

For the foregoing reason, there is a need to solve the above-mentionedproblem by providing a level shifter.

SUMMARY

One embodiment of the present disclosure is to provide a level shifter.The level shifter includes a buffer circuit, a first shift circuit, anda second shift circuit. The buffer circuit provides a first signal and afirst inverted signal of opposite phases. The first shift circuit iselectrically coupled between a first system high voltage terminal and asystem low voltage terminal, and the first shift circuit is configuredto provide a second signal and a second inverted signal of the oppositephases according to the first signal and the first inverted signal. Thefirst shift circuit comprises a plurality of first stacking transistorsand a first voltage divider circuit. The first voltage divider circuitis electrically coupled between the first system high voltage terminaland the system low voltage terminal. The first voltage divider circuitis configured to provide a first inner bias to gate terminals of thefirst stacking transistors. The second shift circuit is electricallycoupled between a second system high voltage terminal and the system lowvoltage terminal, and the second shift circuit generates a plurality ofoutput signals according to the second signal and the second invertedsignal.

The other embodiment of the present disclosure is to provide a levelshifter. The level shifter includes a buffer circuit, a first shiftcircuit and a second shift circuit. The buffer circuit provides a firstsignal and a first inverted signal of opposite phases. The first shiftcircuit is electrically coupled between a first system high voltageterminal and a system low voltage terminal, and the first shift circuitbeing configured to provide a second signal and a second inverted signalof the opposite phases according to the first signal and the firstinverted signal. The second shift circuit is electrically coupledbetween a second system high voltage terminal and the system low voltageterminal. The second shift circuit generates a plurality of outputsignals according to the second signal and the second inverted signal.The first signal and the first inverted signal operate in a positivevoltage domain, and the second signal and the second inverted signaloperate in a negative voltage domain.

In summary, the present disclosure utilizes the first voltage dividercircuit to provide the first inner bias to the first stackingtransistors. In this manner, the circuit area for generating controlsignals is reduced.

It is to be understood that both the foregoing general description andthe following detailed description are by examples, and are intended toprovide further explanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments of the present disclosure and, together with thedescription, serve to explain the principles of the present disclosure.In the drawings,

FIG. 1 depicts a functional block diagram of a circuit according to oneembodiment of the present disclosure;

FIG. 2A depicts a circuit structure diagram of a first shift circuit ofthe level shifter in FIG. 1 ;

FIG. 2B depicts a circuit structure diagram of a second shift circuit ofthe level shifter in FIG. 1 ;

FIG. 3 depicts timing diagrams for an operation of the level shifter inFIG. 2A and FIG. 2B; and

FIG. 4 depicts a schematic structure diagram of an N-type transistor inthe level shifter in FIG. 2A and FIG. 2B.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the presentdisclosure, examples of which are described herein and illustrated inthe accompanying drawings. While the disclosure will be described inconjunction with embodiments, it will be understood that they are notintended to limit the disclosure to these embodiments. Description ofthe operation does not intend to limit the operation sequence. Anystructures resulting from recombination of elements with equivalenteffects are within the scope of the present disclosure. It is notedthat, in accordance with the standard practice in the industry, thedrawings are only used for understanding and are not drawn to scale.Hence, the drawings are not meant to limit the actual embodiments of thepresent disclosure. In fact, the dimensions of the various features maybe arbitrarily increased or reduced for clarity of discussion. Whereverpossible, the same reference numbers are used in the drawings and thedescription to refer to the same or like parts for better understanding.

Throughout the specification and drawings, indexes 1~n may be used inthe reference numbers of components and signals for ease of referring torespective components and signals. The use of indexes 1~n does notintend to restrict the count of components and signals to any specificnumber. In the specification and drawings, if a reference number of aparticular component or signal is used without using the index, it meansthat the reference number is used to refer to any unspecific componentor signal of corresponding component group or signal group.

Furthermore, it should be understood that the terms, “comprising”,“including”, “having”, “containing”, “involving” and the like, usedherein are open-ended, that is, including but not limited to. It will beunderstood that, as used herein, the phrase “and/or” includes any andall combinations of one or more of the associated listed items.

In this document, the term “coupled” may also be termed “electricallycoupled,” and the term “connected” may be termed “electricallyconnected.” “Coupled” and “connected” may also be used to indicate thattwo or more elements cooperate or interact with each other. It will beunderstood that, although the terms “first,” “second,” etc., may be usedherein to describe various elements, these elements should not belimited by these terms. These terms are used to distinguish one elementfrom another. For example, a first element could be termed a secondelement, and, similarly, a second element could be termed a firstelement, without departing from the scope of the embodiments.

A description is provided with reference to FIG. 1 . FIG. 1 depicts afunctional block diagram of a circuit according to one embodiment of thepresent disclosure. As shown in FIG. 1 , a level shifter 100 isconfigured to provide three pairs of output signals VOP1/VON1, VOP2/VON2and VOP3/VON3 to an input/output circuit 200. In one embodiment, theinput/output circuit 200 includes internal circuit elements 210, 220,230. The three internal circuit elements 210, 220, and 230 need tooperate in different voltage domains, respectively. For example, acontrol signal required by the internal circuit element 210 is switchedbetween +9-12 volts (V), 3 \~6 volts, and 0 \~-3 volts. In practicalapplications, the input/output circuit 200 can be used as a buffercircuit in a gate driver.

The input/output circuit 200 is electrically coupled between a secondsystem high voltage terminal VGH and a system low voltage terminal VGL.The input/output circuit 200 uses a potential of the second system highvoltage terminal VGH or a potential of the system low voltage terminalVGL as an output signal VOUT and transmits the output signal VOUT to agate driver in the display panel according to the output signalsVOP1/VON1, VOP2/VON2, and VOP3/VON3, so as to drive light-emittingelements of the display panel 300.

In one embodiment, the level shifter 100 may be configured to providethe output signals VOP1/VON1 with a voltage domain from 8.91 volts to 12volts, the output signals VOP2/VON2 with a voltage domain from 2.92volts to 6.03 volts, and the output signals VOP3/VON3 with a voltagedomain from -3 volts to 0.028 volts.

The level shifter 100 includes a buffer circuit 120, a first shiftcircuit 130, and a second shift circuit 140. The buffer circuit 120 isconfigured to receive an input signal VIN and provide a first signalVSP1 and a first inverted signal VSN1 to the first shift circuit 130.The first signal VSP1 and the first inverted signal VSN1 operate in apositive voltage domain, from 0 volts to 1.8 volts, and the first signalVSP1 and the first inverted signal VSN1 are signals of opposite phases.For example, when the first signal VSP1 is switched from 0 volts to 1.8volts, the first inverted signal VSN1 is switched from 1.8 volts to 0volts.

The first shift circuit 130 is electrically coupled between a firstsystem high voltage terminal VDD and the system low voltage terminalVGL. The first shift circuit 130 is configured to provide a secondsignal VSP2 and a second inverted signal VSN2 to the second shiftcircuit 140 according to the first signal VSP1 and the first invertedsignal VSN1. The second signal VSP2 and the second inverted signal VSN2operate in a negative voltage domain, from -0.58 volts to -3 volts. Thesecond signal VSP2 and the first signal VSP1 are signals of an identicalphase. The second inverted signal VSN2 and the first inverted signalVSN1 are signals of an identical phase. The second inverted signal VSN2has an opposite phase relative to the second signal VSP2. For example,when the first signal VSP1 is switched from 0 volts to 3 volts, thesecond signal VSP2 is switched from -3 volts to -0.58 volts, and thesecond inverted signal VSN2 is switched from -0.58 volts to -3 volts.The detailed operation is further described in the subsequentembodiments.

The second shift circuit 140 is electrically coupled between the secondsystem high voltage terminal VGH and the system low voltage terminalVGL. The second shift circuit 140 is configured to generate the outputsignals VOP1/VON1, VOP2/VON2, and VOP3/VON3 according to the secondsignal VSP2 and the second inverted signal VSN2, and provide the outputsignals VOP1/VON1, VOP2/VON2, and VOP3/VON3 to the input/output circuit200. The output signals VOP1 and VON1 operate in the voltage domain from8.91 volts to 12 volts, the output signals VOP2 and VON2 operate in thevoltage domain from 2.92 volts to 6.03 volts, and the output signalsVOP3 and VON3 operate in the voltage domain from 0.028 volts to -3volts. The second signal VSP2 and the output signals VOP1, VOP2, andVOP3 are signals of the identical phase. The second inverted signal VSN2and the output signals VON1, VON2, and VON3 are signals of the identicalphase. The output signal VON1 and the output signal VOP1 are signals ofthe opposite phases, the output signal VON2 and the output signal VOP2are signals of the opposite phases, and the output signal VON3 and theoutput signals VOP3 are signals of the opposite phases.

For example, when the second inverted signal VSN2 is switched from -0.58volts to -3 volts, the output signal VOP1 is switched from 8.91 volts to12 volts and the output signal VON2 is switched from 6.03 volts to 2.92volts, the output signal VOP2 is switched from 2.92 volts to 6.03 voltsand the output signal VON1 is switched from 12 volts to 8.91 volts, andthe output signal VOP3 is switched from -3 volts to 0.028 volts and theoutput signal VON3 is switched from 0.028 volts to -3 volts. Thedetailed operation is further described in the subsequent embodiments.

In the embodiments of the present disclosure, the potential of thesystem low voltage terminal VGL can be set to a negative value, so as toincrease a shift range of the output signals VOP1, VOP2, and VOP3 of thelevel shifter 100. In another embodiment, when the level shifter 100 isintegrated with and applied to a gate driver, the potential operationinterval of the gate driver can be increased. When the output voltage isset to a negative output voltage, the switches of the display circuitcan be turned off more accurately to reduce the leakage currents. Whenthe output voltage is set to a positive high output voltage, it ishelpful in increasing the driving current of the light-emittingelements.

A description is provided with reference to FIG. 2A and FIG. 2B. FIG. 2Adepicts a circuit structure diagram of the first shift circuit 130 ofthe level shifter 100 in FIG. 1 . FIG. 2B depicts a circuit structurediagram of the second shift circuit 140 of the level shifter 100 in FIG.1 . As shown in FIG. 2A and FIG. 2B, the level shifter 100 includes thebuffer circuit 120, the first shift circuit 130, and the second shiftcircuit 140.

The potential of the second system high voltage terminal VGH is muchhigher than a potential of the first system high voltage terminal VDD,so that the second shift circuit 140 can generate the shifted outputsignal VOP1 and VON1, VOP2 and VON2, VOP3 and VON3 according to thesecond signal VSP2 and the second inverted signal VSN2. In the presentdisclosure, the potential of the second system high voltage terminal VGHis implemented by using 12 volts, the potential of the first system highvoltage terminal VDD is implemented by using 1.8 volts, and thepotential of the system low voltage terminal VGL is implemented by using-3 volts.

It is noted that when the potential of the system low voltage terminalVGL is set to the negative value, the N-type transistor adopted in thelevel shifter 100 can be implemented by an N-type metal oxidesemiconductor with a deep N-well to avoid breakdown of PN junctions ofthe N-type transistor. The deep N-well of the N-type transistor in thelevel shifter 100 is electrically coupled to the second system highvoltage terminal VGH, so that the PN junction of the P-type substrateand the deep N-well is not forward conducted, the PN junction of theP-well and the deep N-well is not forward conducted, and the voltagesacross the PN junctions in the N-type transistor are both within theallowable ranges. In this manner, the system low voltage terminal VGL ofthe level shifter 100 is set to the negative value (for example, -3volts), and the N-type transistor can also withstand cross voltages inthe level shifter 100. In addition, the base terminal of each N-typetransistor of the present disclosure is electrically coupled to itssource terminal to eliminate the body effect.

As shown in FIG. 2A, the first shift circuit 130 includes pull-uptransistors TPU1 and TPU2, first stacking transistors TS11~TS14, firstcross-coupled transistors TC11 and TC12, and a first voltage dividercircuit 132. The first stacking transistors TS13 and TS14 and the firstcross-coupled transistors TC11 and TC12 are N-type transistors. Thepull-up transistors TPU1 and TPU2 and the first stacking transistorsTS11 and TS12 are P-type transistors.

The first voltage divider circuit 132 is electrically coupled betweenthe first system high voltage terminal VDD and the system low voltageterminal VGL. The first voltage divider circuit 132 is configured toprovide a first inner bias VB1.

The pull-up transistors TPU1 and TPU2 are electrically coupled to thefirst system high voltage terminal VDD. The pull-up transistors TPU1 andTPU2 are enabled respectively according to the first signal VSP1 and thefirst inverted signal VSN1.

The first cross-coupled transistors TC11 and TC12 are electricallycoupled to the system low voltage terminal VGL. The first cross-coupledtransistors TC11 and TC12 are enabled respectively according to thesecond inverted signal VSN2 and the second signal VSP2.

The first stacking transistors TS11-TS14 are electrically coupledbetween the pull-up transistors TPU1 and TPU2 and the firstcross-coupled transistors TC11 and TC12. Gate terminals of the firststacking transistors TS11-TS14 are configured to receive the first innerbias VB1.

Each of the above transistors has a first terminal, a second terminal,and a gate terminal (Gate). When the first terminal of one of thetransistors is a drain terminal (source terminal), the second terminalof that transistor is a source terminal (drain terminal).

In greater detail, the first voltage divider circuit 132 includes firstvoltage divider transistors TB11 and TB12. The first voltage dividertransistors TB11 and TB12 are N-type transistors. The first voltagedivider transistors TB11 and TB12 are electrically connected in seriesbetween the first system high voltage terminal VDD and the system lowvoltage terminal VGL. A gate terminal and a drain terminal of each ofthe first voltage divider transistors TB11 and TB12 are electricallycoupled.

The first terminal (source terminal) of the pull-up transistor TPU1 iselectrically coupled to the first system high voltage terminal VDD, thesecond terminal of the pull-up transistor TPU1 is electrically coupledto the first terminal (source terminal) of the first stacking transistorTS11, and the gate terminal of the pull-up transistor TPU1 is configuredto receive the first signal VSP1. The second terminal of the firststacking transistor TS11 is electrically coupled to the first terminalof the first stacking transistor TS13. The gate terminal of the firststacking transistor TS11 is electrically coupled to the gate terminal ofthe first stacking transistor TS13. The gate terminals of the firststacking transistors TS11 and TS13 are configured to receive the firstinner bias VB1.

The second terminal of the first stacking transistor TS13 is configuredto provide the second inverted signal VSN2, and the second terminal ofthe first stacking transistor TS13 is electrically coupled to the firstterminal of the first cross-coupled transistor TC11. The second terminalof the first cross-coupled transistor TC11 is electrically coupled tothe system low voltage terminal VGL. The gate terminal of the firstcross-coupled transistor TC11 is electrically coupled to the secondterminal of the first stacking transistor TS14, and the gate terminal ofthe first cross-coupled transistor TC11 is configured to receive thesecond signal VSP2.

The first terminal (source terminal) of the pull-up transistor TPU2 iselectrically coupled to the first system high voltage terminal VDD, thesecond terminal of the pull-up transistor TPU2 is electrically coupledto the first terminal (source terminal) of the first stacking transistorTS12, and the gate terminal of the pull-up transistor TPU2 is configuredto receive the first inverted signal VSN1. The second terminal of thefirst stacking transistor TS12 is electrically coupled to the firstterminal of the first stacking transistor TS14. The gate terminal of thefirst stacking transistor TS12 is electrically coupled to the gateterminal of the first stacking transistor TS14. The gate terminals ofthe first stacking transistors TS12 and TS14 are configured to receivethe first inner bias VB1.

The second terminal of the first stacking transistor TS14 is configuredto provide the second signal VSP2, and the second terminal of the firststacking transistor TS14 is electrically coupled to the first terminalof the first cross-coupled transistor TC12. The second terminal of thefirst cross-coupled transistor TC12 is electrically coupled to thesystem low voltage terminal VGL. The gate terminal of the firstcross-coupled transistor TC12 is electrically coupled to the secondterminal of the first stacking transistor TS13, and the gate terminal ofthe first cross-coupled transistor TC12 is configured to receive thesecond inverted signal VSN2.

As shown in FIG. 2B, the second shift circuit 140 includes pull-downtransistors TPD1 and TPD2, second stacking transistors TS21-TS28, thirdstacking transistors TS31-TS38, second cross-coupled transistors TC21and TC22, and a second voltage divider circuit 142. The pull-downtransistors TPD1 and TPD2, the second stacking transistors TS23, TS24,TS27, TS28, and the third stacking transistors TS33, TS34, TS37, TS38are N-type transistors. The second cross-coupled transistors TC21 andTC22, the second stacking transistors TS21, TS22, TS25, TS26, and thethird stacking transistors TS31, TS32, TS35, TS36 are P-typetransistors.

The second voltage divider circuit 142 is electrically coupled betweenthe second system high voltage terminal VGH and a ground terminal GND.The second voltage divider circuit 142 includes second voltage dividertransistors TB21 and TB22 and third voltage divider transistors TB31 andTB32. The second voltage divider transistors TB21 and TB22 areelectrically coupled between the second system high voltage terminal VGHand a node N1. The third voltage divider transistors TB31 and TB32 areelectrically coupled between the node N1 and the ground terminal GND.The second voltage divider circuit 142 includes the second voltagedivider transistors TB21 and TB22 and the third voltage dividertransistors TB31 and TB32, which are N-type transistors. The secondvoltage divider transistors TB21 and TB22 in the second voltage dividercircuit 142 are configured to provide second inner biases VB2 and VB3.The third voltage divider transistors TB31 and TB32 in the secondvoltage divider circuit 142 are configured to provide second innerbiases VB4 and VB5.

The second cross-coupled transistors TC21 and TC22 are electricallycoupled between the second system high voltage terminal VGH and twofirst output terminals. The two first output terminals are respectivelyconfigured to output the output signals VOP1 and VON1. The outputsignals VOP1 and VON1 operate in the same voltage domain, and the outputsignal VON1 and the output signal VOP1 are signals of the oppositephases. The second cross-coupled transistor TC21 is enabled according tothe output signal VON1, and the second cross-coupled transistor TC22 isenabled according to the output signal VOP1.

The second stacking transistors TS21~TS28 are electrically coupledbetween the two first output terminals and two second output terminals.The two second output terminals are respectively configured to outputthe output signals VOP2 and VON2. The output signals VOP2 and VON2operate in the same voltage domain, and the output signal VON2 and theoutput signal VOP2 are signals of the opposite phases. Gate terminals ofthe second stacking transistors TS21~TS24 are configured to receive thesecond inner bias VB2. Gate terminals of the second stacking transistorsTS25~TS28 are configured to receive the second inner bias VB3.

The third stacking transistors TS31~TS38 are electrically coupledbetween the two second output terminals and two third output terminals.The two third output terminals are respectively configured to output theoutput signals VOP3 and VON3. The output signals VOP3 and VON3 operatein the same voltage domain, and the output signal VON3 and the outputsignal VOP3 are signals of the opposite phases. Gate terminals of thethird stacking transistors TS31~TS34 are configured to receive thesecond inner bias VB4. Gate terminals of the third stacking transistorsTS35~TS38 are configured to receive the second inner bias VB5.

The pull-down transistors TPD1 and TPD2 are electrically coupled betweenthe two third output terminals and the system low voltage terminal VGL.The pull-down transistors TPD1 and TPD2 are enabled respectivelyaccording to the second inverted signal VSN2 and the second signal VSP2.

In greater detail, the second voltage divider circuit 142 includessecond voltage divider transistors TB21 and TB22 and third voltagedivider transistors TB31 and TB32. The second voltage dividertransistors TB21 and TB22 and the third voltage divider transistors TB31and TB32 are electrically connected in series between the second systemhigh voltage terminal VGH and the ground terminal GND. A gate terminaland a drain terminal of each of the second voltage divider transistorsTB21 and TB22 and the third voltage divider transistors TB31 and TB32are electrically coupled.

A first terminal of the second cross-coupled transistor TC21 iselectrically coupled to the second system high voltage terminal VGH. Asecond terminal of the second cross-coupled transistor TC21 iselectrically coupled to a first terminal of the second stackingtransistor TS21. A gate terminal of the second cross-coupled transistorTC21 is configured to receive the output signal VON1. That is, thesecond cross-coupled transistor TC21 is enabled according to the outputsignal VON1.

A second terminal of the second stacking transistor TS21 is electricallycoupled to a first terminal of the second stacking transistor TS23. Agate terminal of the second stacking transistor TS21 is electricallycoupled to a gate terminal of the second stacking transistor TS23. Thegate terminals of the second stacking transistors TS21 and TS23 areconfigured to receive the second inner bias VB2.

A first terminal of the second stacking transistor TS25 is electricallycoupled to a second terminal of the second stacking transistor TS23. Asecond terminal of the second stacking transistor TS25 is electricallycoupled to a first terminal of the second stacking transistor TS27. Agate terminal of the second stacking transistor TS25 is electricallycoupled to a gate terminal of the second stacking transistor TS27. Thegate terminals of the second stacking transistors T25 and TS27 areconfigured to receive the second inner bias VB3.

A first terminal of the third stacking transistor TS31 is electricallycoupled to a second terminal of the second stacking transistor TS27. Asecond terminal of the third stacking transistor TS31 is electricallycoupled to a first terminal of the third stacking transistor TS33. Agate terminal of the third stacking transistor TS31 is electricallycoupled to a gate terminal of the third stacking transistor TS33. Thegate terminals of the third stacking transistor TS31 and TS33 areconfigured to receive the second inner bias VB4.

A first terminal of the third stacking transistor TS35 is electricallycoupled to a second terminal of the second stacking transistor TS33. Asecond terminal of the third stacking transistor TS35 is electricallycoupled to a first terminal of the third stacking transistor TS37. Agate terminal of the third stacking transistor TS35 is electricallycoupled to a gate terminal of the third stacking transistor TS37. Thegate terminals of the third stacking transistors T35 and TS37 areconfigured to receive the second inner bias VB5.

A first terminal of the pull-down transistor TPD1 is electricallycoupled to a second terminal of the third stacking transistor TS37. Asecond terminal of the pull-down transistor TPD1 is electrically coupledto the system low voltage terminal VGL. A gate terminal of the pull-downtransistor TPD1 is configured to receive the second inverted signalVSN2.

A first terminal of the second cross-coupled transistor TC22 iselectrically coupled to the second system high voltage terminal VGH. Asecond terminal of the second cross-coupled transistor TC22 iselectrically coupled to a first terminal of the second stackingtransistor TS22. A gate terminal of the second cross-coupled transistorTC22 is configured to receive the output signal VOP1. That is, thesecond cross-coupled transistor TC22 is enabled according to the outputsignal VOP1.

A second terminal of the second stacking transistor TS22 is electricallycoupled to a first terminal of the second stacking transistor TS24. Agate terminal of the second stacking transistor TS22 is electricallycoupled to a gate terminal of the second stacking transistor TS24. Thegate terminals of the second stacking transistors T22 and TS24 areconfigured to receive the second inner bias VB2.

A first terminal of the second stacking transistor TS26 is electricallycoupled to a second terminal of the second stacking transistor TS24. Asecond terminal of the second stacking transistor TS26 is electricallycoupled to a first terminal of the second stacking transistor TS28. Agate terminal of the second stacking transistor TS26 is electricallycoupled to a gate terminal of the second stacking transistor TS28. Thegate terminals of the second stacking transistors TS26 and TS28 areconfigured to receive the second inner bias VB3.

A first terminal of the third stacking transistor TS32 is electricallycoupled to a second terminal of the second stacking transistor TS28. Asecond terminal of the third stacking transistor TS32 is electricallycoupled to a first terminal of the third stacking transistor TS34. Agate terminal of the third stacking transistor TS32 is electricallycoupled to a gate terminal of the third stacking transistor TS34. Thegate terminals of the third stacking transistor TS32 and TS34 areconfigured to receive the second inner bias VB4.

A first terminal of the third stacking transistor TS36 is electricallycoupled to a second terminal of the third stacking transistor TS34. Asecond terminal of the third stacking transistor TS36 is electricallycoupled to a first terminal of the third stacking transistor TS38. Agate terminal of the third stacking transistor TS36 is electricallycoupled to a gate terminal of the third stacking transistor TS38. Thegate terminals of the third stacking transistors T36 and TS38 areconfigured to receive the second inner bias VB5.

A first terminal of the pull-down transistor TPD2 is electricallycoupled to a second terminal of the third stacking transistor TS38. Asecond terminal of the pull-down transistor TPD2 is electrically coupledto the system low voltage terminal VGL. A gate terminal of the pull-downtransistor TPD2 is configured to receive the second signal VSP2.

A description is provided with reference to FIG. 3 . FIG. 3 depictstiming diagrams for an operation of the level shifter in FIG. 2A andFIG. 2B. FIG. 3 depicts timing diagrams of the input signal VIN, thefirst signal VSP1, the first inverted signal VSN1, the second signalVSP2, the second inverted signal VSN2, and the output signals VOP1~VOP3and VON1~VON3 in the level shifter 100 in FIG. 2A and FIG. 2B from atime point t1 to a time point t5.

As shown in FIG. 3 , the input signal VIN is operated (switched) between0 and 1.8 volts. The first signal VSP1 and the first inverted signalVSN1 are operated (switched) in a positive voltage domain (0 \~3V). Thesecond signal VSP2 and the second inverted signal VSN2 are operated(switched) in the negative voltage domain (-0.58 \~-3V).

When the input voltage VIN is at 1.8 volts, the first signal VSP1 andthe second signal VSP2 are at 3 volts and -0.58 volts, respectively, andthe first inverted signal VSN1 and the second inverted signal VSN2 areat 0 volts and -3 volts, respectively. When the input voltage VIN is at0 volts, the first signal VSP1 and the second signal VSP2 are at 0 voltsand -3 volts, respectively, and the first inverted signal VSN1 and thesecond inverted signal VSN2 are at 3 volts and -0.58 volts,respectively.

It is noted that the first voltage divider transistor TB11 will transmitthe potential of the first system high voltage terminal VDD (1.8 V) to asecond terminal of the first voltage divider transistor TB11 until apotential of the gate terminal of the first voltage divider transistorTB11 reaches a potential of its source terminal plus a thresholdvoltage, the first voltage divider transistor TB11 is then cut off. Thatis to say, if the threshold voltage of the first voltage dividertransistor TB11 is 2.4 volts, a potential of the second terminal of thefirst voltage divider transistor TB11 will be at -0.6 volts. That is,the first inner bias VB1 is -0.6 volts.

Additionally, the second voltage divider transistor TB21 will transmitthe potential of the second system high voltage terminal VGH (12 V) to asecond terminal of the second voltage divider transistor TB21 until apotential of the gate terminal of the second voltage divider transistorTB21 reaches a potential of its source terminal plus a thresholdvoltage, the second voltage divider transistor TB21 is then cut off.That is to say, if the threshold voltage of the second voltage dividertransistor TB21 is 3 volts, a potential of the second terminal of thesecond voltage divider transistor TB21 will be at 9 volts. That is, thesecond inner bias VB1 is 9 volts. Similarly, it can be deduced that thesecond inner biases VB3, VB4, and VB5 are 6 volts, 3 volts, and 0 volts,respectively.

Between the time points t1 and t2, when a level of the input signal VINis switched from 1.8 volts before the time point t1 to 0 volts, thebuffer circuit 120 provides the 3 volt first inverted signal VSN1 to thepull-up transistor TPU2 and provides the 0 volt first signal VSP1 to thepull-up transistor TPU1, so that the pull-up transistor TPU2 is turnedoff and the pull-up transistor TPU1 is turned on.

Turning on the pull-up transistor TPU1 will transmit the potential ofthe first system high voltage terminal VDD (1.8 V) to the first terminalof the first stacking transistor TS11.

Since a potential of the first terminal (source terminal) of the firststacking transistor TS11 is at 1.8 volts and the gate terminal of thefirst stacking transistor TS11 receives the first inner bias VB1 (-0.6V), the first stacking transistor TS11 is turned on and transmits thepotential of the first system high voltage terminal VDD (1.8 V) to thefirst terminal of the first stacking transistor TS13.

Since the gate terminal of the first stacking transistor TS13 receivesthe first inner bias VB1 (-0.6 V), a potential of the second terminal ofthe first stacking transistor TS13 will rise until the first stackingtransistor TS13 is cut off. At this time, the potential of the secondterminal of the first stacking transistor TS13 is approximately -0.58volts. In this manner, the potential of -0.58 volts is used as thesecond inverted signal VSN2 and transmitted to the gate terminal of thepull-down transistor TPD1 in the second shift circuit 140.

The second inverted signal VSN2 that is at -0.58 volts turns on thefirst cross-coupled transistor TC12, so that the first cross-coupledtransistor TC12 transmits the potential of the system low voltageterminal VGL (-3 V) to the first terminal of the first cross-coupledtransistor TC12, and the potential of the system low voltage terminalVGL (-3 V) is used as the second signal VSP2 and is output. The secondsignal VSP2 that is at -3 volts turns off the first cross-coupledtransistor TC11.

Since the second terminal (source terminal) of the first stackingtransistor TS14 is at -3 volts and the gate terminal of the firststacking transistor TS14 receives the first inner bias VB1 (-0.6 V), thefirst stacking transistor TS14 is turned on to transmit the potential ofthe system low voltage terminal VGL (-3 V) to the first terminal of thefirst stacking transistor TS14.

Since the second terminal of the first stacking transistor TS12 is at -3volts and the gate terminal of the first stacking transistor TS12receives the first inner bias VB1 (-0.6 V), a potential of the firstterminal of the first stacking transistor TS12 will drop until the firststacking transistor TS12 is cut off. At this time, the potential of thefirst terminal of the first stacking transistor TS12 is approximately-0.58 volts.

Therefore, between the time points t1 and t2, when the level of theinput signal VIN is switched from the 1.8 volts before the time point t1to 0 volts, the first shift circuit 130 provides the second signal VSP2with the potential of -3 volts to the gate terminal of the pull-downtransistor TPD2 and provides the second inverted signal VSN2 with thepotential of -0.58 volts to the gate terminal of the pull-downtransistor TPD1, so that the pull-down transistor TPD1 is turned on andthe pull-down transistor TPD2 is turned off.

Turning on the pull-down transistor TPD1 will transmit the potential ofthe system low voltage terminal VGL (-3 V) to the second terminal(source terminal) of the third stacking transistor TS37, and thepotential of -3 V is used as the output signal VOP3 and is output.

Since the second terminal (source terminal) of the third stackingtransistor TS37 is at -3 volts and the gate terminal of the thirdstacking transistor TS37 receives the second inner bias VB5 (0 V), thethird stacking transistor TS37 is turned on and transmits the potentialof the system low voltage terminal VGL (-3 V) to the second terminal ofthe third stacking transistor TS35.

Since the gate terminal of the third stacking transistor TS35 receivesthe second inner bias VB5 (0 V), a potential of the first terminal(source terminal) of the third stacking transistor TS35 will drop untilthe third stacking transistor TS35 is cut off. At this time, thepotential of the first terminal (source terminal) of the third stackingtransistor TS35 is approximately -0.07 volts.

Since the gate terminal of the third stacking transistor TS33 receivesthe second inner bias VB4 (3 V), the third stacking transistor TS33 isturned on to transmit the potential of the first terminal of the thirdstacking transistor TS35 to the first terminal of the third stackingtransistor TS33.

Since the gate terminal of the third stacking transistor TS31 receivesthe second inner bias VB4 (3 V), a potential of the first terminal(source terminal) of the third stacking transistor TS31 will drop untilthe third stacking transistor TS31 is cut off. At this time, thepotential of the first terminal of the third stacking transistor TS31 isapproximately 2.92 volts, and the potential of 2.92 volts is used as theoutput signal VOP2 and is output.

Since the second terminal (source terminal) of the second stackingtransistor TS27 is at 2.92 volts and the gate terminal of the secondstacking transistor TS27 receives the second inner bias VB1 (6 V), thesecond stacking transistor TS27 is turned on to transmit a potential ofthe second terminal of the second stacking transistor TS27 (2.92 volts)to the first terminal of the second stacking transistor TS27.

Since the gate terminal of the second stacking transistor TS25 receivesthe second inner bias VB3 (6 V), a potential of the first terminal(source terminal) of the second stacking transistor TS25 will drop untilthe second stacking transistor TS25 is cut off. At this time, thepotential of the first terminal of the second stacking transistor TS25is approximately 5.92 volts.

Since the second terminal (source terminal) of the second stackingtransistor TS23 is at 5.92 volts and the gate terminal of the secondstacking transistor TS23 receives the second inner bias VB2 (9 V), thesecond stacking transistor TS23 is turned on to transmit the potentialof the first terminal of the second stacking transistor TS25 (5.92volts) to the first terminal of the second stacking transistor TS23.

Since the gate terminal of the second stacking transistor TS21 receivesthe second inner bias VB2 (9 V), a potential of the first terminal(source terminal) of the second stacking transistor TS21 will drop untilthe second stacking transistor TS21 is cut off. At this time, thepotential of the first terminal of the second stacking transistor TS21is approximately 8.91 volts, and the potential of 8.91 volts is used asthe output signal VOP1 and is output.

The output signal VOP1 that is at 8.91 volts turns on the secondcross-coupled transistor TC22, so that the second cross-coupledtransistor TC22 transmits the potential of the second system highvoltage terminal VGH (12 V) to the second terminal of the secondcross-coupled transistor TC22, and the potential of the second systemhigh voltage terminal VGH (12 V) is used as output signal VON1 and isoutput. The output signal VON1 that is at 12 volts turns off the secondcross-coupled transistor TC21.

Since the first terminal (source terminal) of the second stackingtransistor TS22 is at 12 volts and the gate terminal of the secondstacking transistor TS22 receives the second inner bias VB2 (9 V), thesecond stacking transistor TS22 is turned on and transmits the potentialof the second system high voltage terminal VGH (12 V) to the secondterminal of the second stacking transistor TS22 (2.92 volts).

Since the gate terminal of the second stacking transistor TS24 receivesthe second inner bias VB2 (9 V), a potential of the second terminal(source terminal) of the second stacking transistor TS24 will rise untilthe second stacking transistor TS24 is cut off. At this time, thepotential of the second terminal of the second stacking transistor TS24is approximately 9.03 volts.

Since the first terminal (source terminal) of the second stackingtransistor TS26 is at 9.03 volts and the gate terminal of the secondstacking transistor TS26 receives the second inner bias VB3 (6 V), thesecond stacking transistor TS26 is turned on to transmit a potential ofthe first terminal of the second stacking transistor TS26 (9.03 volts)to the second terminal of the second stacking transistor TS26.

Since the gate terminal of the second stacking transistor TS28 receivesthe second inner bias VB3 (6 V), a potential of the second terminal(source terminal) of the second stacking transistor TS28 will rise untilthe second stacking transistor TS28 is cut off. At this time, thepotential of the second terminal of the second stacking transistor TS28is approximately 6.03 volts, and the potential of 6.03 volts is used asthe output signal VON2 and is output.

Since the first terminal (source terminal) of the third stackingtransistor TS32 is at 6.03 volts and the gate terminal of the thirdstacking transistor TS32 receives the second inner bias VB4 (3 V), thethird stacking transistor TS32 is turned on to transmit a potential ofthe first terminal of the third stacking transistor TS32 (6.03 volts) tothe first terminal of the third stacking transistor TS34.

Since the gate terminal of the third stacking transistor TS34 receivesthe second inner bias VB4 (3 V), a potential of the second terminal(source terminal) of the third stacking transistor TS34 will rise untilthe third stacking transistor TS34 is cut off. At this time, thepotential of the second terminal of the third stacking transistor TS34is approximately 3.03 volts.

Since the first terminal (source terminal) of the third stackingtransistor TS36 is at 3.03 volts and the gate terminal of the thirdstacking transistor TS36 receives the second inner bias VB5 (0 V), thethird stacking transistor TS36 is turned on to transmit a potential ofthe first terminal of the third stacking transistor TS36 (3.03 volts) tothe second terminal of the third stacking transistor TS36.

Since the gate terminal of the third stacking transistor TS38 receivesthe second inner bias VB5 (0 V), a potential of the second terminal(source terminal) of the third stacking transistor TS38 will rise untilthe third stacking transistor TS38 is cut off. At this time, thepotential of the second terminal of the third stacking transistor TS38is approximately 0.028 volts, and the potential of 0.028 volts is usedas the output signal VON3 and is output.

When the level of the input signal VIN is switched from 0 volts to 1.8volts, the output signals VOP1, VOP2, VOP3, VON1, VON2 and VON3 of thelevel shifter 100 are at 12 volts, 6.03 volts, 0.028 volts, 8.91 volts,2.92 volts and -3 volts, respectively. When the level of the inputsignal VIN is switched from 0 volts to 1.8 volts, the operation methodof the level shifter 100 is in mirror symmetry to the operation methodwhen the level of the input signal VIN is switched from 1.8 volts to 0volts. Therefore, a description in this regard is not repeated here.

As a result, the output signals VOP1 and VON1 are switched between 12and 8.91 volts. The output signals VOP2 and VON2 are switched between6.03 and 2.92 volts. The output signals VOP3 and VON3 are switchedbetween 0.028 and -3 volts.

A description is provided with reference to FIG. 4 . FIG. 4 depicts aschematic structure diagram of an N-type transistor in the level shifter100 in FIG. 2A and FIG. 2B. As shown in FIG. 4 , the N-type transistorwith an N-well includes a number of n+ areas 410, a p+ area 420, aP-well 430, a deep N-well 440, and a P-type substrate 450.

In addition to that, D, G, B and S in FIG. 4 respectively represent thedrain terminal, the gate terminal, the base terminal, and the sourceterminal of the transistor. As shown in FIG. 4 , the base terminal B inthe transistor is electrically coupled to the source terminal S toeliminate the body effect. In addition, the deep N-well 440 iselectrically coupled to the second system high voltage terminal VGH toavoid breakdown of the PN junctions of the transistor when operating ina negative voltage domain, thus setting the potential of the system lowvoltage terminal VGL to -3 volts.

In summary, the level shifter 100 utilizes the two-stage first shiftcircuit 130 and second shift circuit 140 to output the shifted outputsignals VOP1, VON1, VOP2, VON2, VOP3, and VON3, so as to increase theshift range of the output signals VOP1, VON1, VOP2, VON2, VOP3, VON3.Additionally, by electrically coupling the deep N-well of the N-typemetal oxide semiconductor with the deep N-well to the second system highvoltage terminal VGH, the system low voltage terminal VGL can be set toa negative value. The PN junctions of the transistor do not break downto increase the shift range of the output signals VOP1, VON1, VOP2,VON2, VOP3, VON3 of the level shifter 100. In addition to that, thepresent disclosure utilizes the first voltage divider circuit 132 andthe second voltage divider circuit 142 to provide the first inner biasVB1 and the second internal biases VB2~VB5, thus reducing the circuitarea for generating control signals.

Although the present disclosure has been described in considerabledetail with reference to certain embodiments thereof, other embodimentsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the embodiments containedherein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentdisclosure without departing from the scope or spirit of the presentdisclosure. In view of the foregoing, it is intended that the presentdisclosure cover modifications and variations of this disclosureprovided they fall within the scope of the following claims and theirequivalents.

What is claimed is:
 1. A level shifter comprising: a buffer circuitproviding a first signal and a first inverted signal of opposite phases;a first shift circuit electrically coupled between a first system highvoltage terminal and a system low voltage terminal, and the first shiftcircuit being configured to provide a second signal and a secondinverted signal of the opposite phases according to the first signal andthe first inverted signal; and a second shift circuit electricallycoupled between a second system high voltage terminal and the system lowvoltage terminal, wherein the second shift circuit generates a pluralityof output signals according to the second signal and the second invertedsignal, wherein the first signal and the first inverted signal operatein a positive voltage domain, and wherein the second signal and thesecond inverted signal operate in a negative voltage domain.
 2. Thelevel shifter of claim 1, wherein the first shift circuit comprises: aplurality of first stacking transistors; and a first voltage dividercircuit, electrically coupled between the first system high voltageterminal and the system low voltage terminal, and being configured toprovide a first inner bias to gate terminals of the first stackingtransistors.
 3. The level shifter of claim 2, wherein the first shiftcircuit further comprises: two pull-up transistors electrically coupledto the first system high voltage terminal, the two pull-up transistorsbeing enabled respectively according to the first signal and the firstinverted signal; two first cross-coupled transistors electricallycoupled to the system low voltage terminal, the two first cross-coupledtransistors being enabled respectively according to the second signaland the second inverted signal; and a plurality of first stackingtransistors, electrically coupled between the two pull-up transistorsand the two first cross-coupled transistors.
 4. The level shifter ofclaim 3, wherein each of the two first cross-coupled transistors isimplemented by an N-type metal oxide semiconductor with a deep N-well,wherein the deep N-well of each of the two first cross-coupledtransistors is electrically coupled to the second system high voltageterminal, wherein a base terminal and a source terminal of each of thetwo first cross-coupled transistors are electrically coupled.
 5. Thelevel shifter of claim 3, wherein the first voltage divider circuitcomprises: two first voltage divider transistors electrically coupledbetween the first system high voltage terminal and the system lowvoltage terminal, the two first voltage divider transistors beingconfigured to provide the first inner bias to the gate terminals of thefirst stacking transistors.
 6. The level shifter of claim 1, wherein thesecond shift circuit comprises: a second voltage divider circuitelectrically coupled between the second system high voltage terminal anda ground terminal, and being configured to provide a plurality of secondinner biases.
 7. The level shifter of claim 6, wherein a voltage of thesystem low voltage terminal is lower than a voltage of the groundterminal.
 8. The level shifter of claim 6, wherein the second shiftcircuit further comprises: two second cross-coupled transistorselectrically coupled between the second system high voltage terminal andtwo first output terminals; a plurality of second stacking transistorselectrically coupled between the two first output terminals and twosecond output terminals, the second stacking transistors beingconfigured to respectively receive one part of the second inner biases;a plurality of third stacking transistors electrically coupled betweenthe two second output terminals and two third output terminals, thethird stacking transistors being configured to respectively receiveanother part of the second inner biases; and two pull-down transistorselectrically coupled between the two third output terminals and thesystem low voltage terminal, the two pull-down transistors being enabledaccording to the second signal and the second inverted signal, whereinthe two first output terminals, the two second output terminals, and thetwo third output terminals are configured to output the output signals.9. The level shifter of claim 8, wherein the second voltage dividercircuit comprises: a plurality of second voltage divider transistorselectrically coupled between the second system high voltage terminal anda node, the second voltage divider transistors being configured toprovide the part of the second inner biases to gate terminals of thesecond stacking transistors; and a plurality of third voltage dividertransistors electrically coupled between the node and the groundterminal, the third voltage divider transistors being configured toprovide the another part of the second inner biases to gate terminals ofthe third stacking transistors.
 10. The level shifter of claim 1,wherein a voltage of the second system high voltage terminal is higherthan a voltage of the first system high voltage terminal.